Repeat Exercise 12 , but instead write the class within a package that contains an implementation of the ADT bag. Set and get methods will be necessary.

In a doubly linked chain, each node can reference the previous node as well as the next node. Figure 3-11  shows a doubly linked chain and its head reference. Define a class to represent a node in a doubly linked chain. Write the class as an inner class of a class that implements the ADT bag. You can omit set and get methods.

firstNode